1. Field of the Invention
Exemplary embodiments of the present invention relate to a method and an apparatus for transmitting and receiving a multiplexed packet stream through a single transmission channel.
2. Description of Related Art
With the popularization of an IP network, media streaming for transmitting audio/video media streams through an IP network has been widely used. Currently, according to a media streaming transmission scheme widely used in an IP network, separate port numbers are assigned to respective audio or video streams, and the respective streams are transmitted through completely independent transmission channels.
However, it is a frequent occurrence that the number of audio and video streams constituting one contents presentation such as a 3D video increases. Here, the contents presentation stands for one contents consumption unit that is finally consumed by a user, and is configured by audio and video streams, a caption information stream synchronized with a specified time and a metadata stream synchronized with an audio/video. In this case, independent port numbers should be respectively allocated to audio streams, video streams and data streams which constitute one contents presentation, and according to this fact, independent transmission channels based on a number of port numbers are needed.
Also, as the number of contents transmitted to a terminal of a contents consumer increases as in an IPTV-based application for providing a plurality of channels, the number of port numbers needed for providing a service markedly increases.
In order to prevent waste of port numbers as limited resources, a method has been used in which signaling data for initializing and controlling a plurality of audio data, video data, data streams and contents presentations are multiplexed and transmitted to a single transmission channel using one port number. At this time, packet headers with identifiers (IDs) for identifying respective streams are added to a multiplexed packet stream. Hereafter, respective audio, video and data streams constituting a multiplexed packet stream will be defined as substreams.
In the case where a plurality of substreams are multiplexed and transmitted through one transmission channel, substreams with different transmission characteristics or requirements may be multiplexed as one packet stream. For example, since a signaling data substream includes initialization information of a video decoder, all packets of the signaling data substream should be transmitted without the loss of even one packet. Conversely, in the case of a video substream, it is the norm that, even when packet loss occurs to some extent, a serious problem likely to interrupt an entire contents reproduction system is not caused except momentary deterioration of image quality. Rather, in this case, if it is attempted to recover packet loss through retransmission, a delay may occur in the reception of video data.
As a consequence, it is general that respective substreams included in a multi-packet stream, which share one port, have different characteristics with respect to packet loss. In other words, in the multi-packet stream, various kinds of substreams exist from an error-free substream in which no packet loss should be ensured to a substream which should not undergo a packet loss level of a general transmission channel.
Accordingly, in order to achieve a successful single port-based contents presentation using a multi-packet stream, methods for recovering packet should be able to be selected for respective substreams. Namely, while perfect retransmission should be possible for all packet loss in the case a substream in which no packet loss should be ensured, no recovery should be tried for packet loss and transmission should be performed within a preset time in the case of another substream. Further, in a specified substream, recovery for packet loss may be tried within a range not causing a delay longer than a predetermined level between a transmitting end and a receiving end.
As a result, in the case of transmitting a multi-packet stream generated by multiplexing a plurality of substreams, through one transmission channel, it should be possible to select different error correction schemes for respective substreams.